SAP Scripting VBA automative choosing a sap system

I am writing the VBA program which extract data from SAP to Excel and everything goes well. I want automate the whole process and opening a Sap Logon by VBA that's not a problem, but in our company there are many systems based on SAP, so between opening the SAP Logon and the authorization there is a window where i should select a server (screen). Do you know how can i automate server choosing by VBA?